On 29. 05. 24, 23:29, Nathan Chancellor wrote:
Work for __counted_by on generic pointers in structures (not just flexible array members) has started landing in Clang 19 (current tip of tree). During the development of this feature, a restriction was added to __counted_by to prevent the flexible array member's element type from including a flexible array member itself such as:
struct foo { int count; char buf[]; };
struct bar { int count; struct foo data[] __counted_by(count); };
because the size of data cannot be calculated with the standard array size formula:
sizeof(struct foo) * count
This restriction was downgraded to a warning but due to CONFIG_WERROR, it can still break the build. The application of __counted_by on the ports member of 'struct mxser_board' triggers this restriction, resulting in:
drivers/tty/mxser.c:291:2: error: 'counted_by' should not be applied to an array with element of unknown size because 'struct mxser_port' is a struct type with a flexible array member.
Huh -- what am I missing:
struct mxser_port { struct tty_port port; struct mxser_board *board;
unsigned long ioaddr; unsigned long opmode_ioaddr;
u8 rx_high_water; u8 rx_low_water; int type; /* UART type */
u8 x_char; /* xon/xoff character */ u8 IER; /* Interrupt Enable Register */ u8 MCR; /* Modem control register */ u8 FCR; /* FIFO control register */
struct async_icount icount; unsigned int timeout;
u8 read_status_mask; u8 ignore_status_mask; u8 xmit_fifo_size;
spinlock_t slock; };
?
This will be an error in a future compiler version [-Werror,-Wbounds-safety-counted-by-elt-type-unknown-size] 291 | struct mxser_port ports[] __counted_by(nports); | ^~~~~~~~~~~~~~~~~~~~~~~~~ 1 error generated.
Remove this use of __counted_by to fix the warning/error. However, rather than remove it altogether, leave it commented, as it may be possible to support this in future compiler releases.
This looks like a compiler bug/deficiency.
What does gcc say BTW?
Cc: stable@vger.kernel.org Closes: https://github.com/ClangBuiltLinux/linux/issues/2026 Fixes: f34907ecca71 ("mxser: Annotate struct mxser_board with __counted_by")
I would not say "Fixes" here. It only works around a broken compiler.
Signed-off-by: Nathan Chancellor nathan@kernel.org
drivers/tty/mxser.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/drivers/tty/mxser.c b/drivers/tty/mxser.c index 458bb1280ebf..5b97e420a95f 100644 --- a/drivers/tty/mxser.c +++ b/drivers/tty/mxser.c @@ -288,7 +288,7 @@ struct mxser_board { enum mxser_must_hwid must_hwid; speed_t max_baud;
- struct mxser_port ports[] __counted_by(nports);
- struct mxser_port ports[] /* __counted_by(nports) */; };
static DECLARE_BITMAP(mxser_boards, MXSER_BOARDS);
thanks,